blk-mq: fix potential hang if rolling wakeup depth is too high

We currently divide the queue depth by 4 as our batch wakeup count, but we split the wakeups over BT_WAIT_QUEUES number of wait queues. This defaults to 8. If the product of the resulting batch wake count and BT_WAIT_QUEUES is higher than the device queue depth, we can get into a situation where a task goes to sleep waiting for a request, but never gets woken up. Reported-by: Bart Van Assche <[email protected]> Fixes: 4bb659b Cc: [email protected] Signed-off-by: Jens Axboe <[email protected]>
mrcsosa · Oct 7, 2014 · abab13b · abab13b
1 parent d8f429e
commit abab13b
Showing 1 changed file with 2 additions and 2 deletions.
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
@@ -455,8 +455,8 @@ static void bt_update_count(struct blk_mq_bitmap_tags *bt,
 	}
 
 	bt->wake_cnt = BT_WAIT_BATCH;
-	if (bt->wake_cnt > depth / 4)
-		bt->wake_cnt = max(1U, depth / 4);
+	if (bt->wake_cnt > depth / BT_WAIT_QUEUES)
+		bt->wake_cnt = max(1U, depth / BT_WAIT_QUEUES);
 
 	bt->depth = depth;
 }